Documents have come to light which suggest parts of Truman Capote's In Cold Blood – which led the way for the non-fiction novel – played with the truth.

The files, originally held by the Kansas Bureau of Investigations and first reported on by The Wall Street Journal, suggest that Capote may have cast lead investigator Alvin Dewey in a more flattering light than he deserved.

There has long been debate over whether Capote changed facts to suit his work, which detailed the real-life investigation behind the brutal murder of a family in Kansas in 1959.

Capote himself called the book "immaculately factual", but new evidence suggests that events described in the book are different from what actually happened.

In the book, Capote says an agent was sent immediately to follow up a tip-off that the killers might be Perry Smith and Richard Hickock. KBI documents suggest, however, that Dewey waited five days before he followed up on the lead.

In Cold Blood paints Dewey as the brilliant leader of the investigation. Dewey helped Capote considerably with his research, giving him access to the diary of 16-year-old Nancy Clutter, whose final entry was written moments before she was murdered.

Dewey also opened up the KBI case file to Capote and helped him obtain a Kansas driver's license.

The Wall Street Journal also discovered that as part of his contract with Columbia Pictures on a film adaptation of the book, Capote required the film studio to hire Mr Dewey's wife as a consultant.

The KBI has refused to explain the delay in following up the tip Dewey was given and since the book's publication in 1966, they have consistently supported the book's accuracy.

Capote regularly played with the truth in his many stories and was the author of several works of fiction including Breakfast at Tiffany's. In Cold Blood is now considered a modern classic and pioneered long-form journalism and non-fiction novels.

Smith and Hickock's bodies were exhumed recently after prosecutors in Florida claimed they may have been responsible for another family's murder. The two were hanged in 1965 after spending five years on death row.